1. Technical Field
The present invention relates to a method of measuring a gate capacitance of a MOS transistor. Particularly, the present invention relates to a method of measuring an accurate gate capacitance by detecting a measurement error of an LCR meter used to analyze the characteristics of a MOS transistor.
2. Description of the Related Art
A MOS transistor operates on a principle that electric charges accumulate in a channel after passing through a gate oxide layer. Thus, to determine the characteristics of the MOS transistor, a method of measuring a gate capacitance has been widely used.
By measuring the gate capacitance, the amount of electric charge accumulated in the channel of the transistor and the thickness of the gate oxide layer can be obtained. For this reason, the gate capacitance is a critical value that requires precise measurement.
An LCR meter is an apparatus broadly used for measuring a gate capacitance of a MOS transistor. The LCR meter is used to measure parameters, such as a capacitance, an inductance, and a dissipation factor, with high accuracy in a short amount of time. Also, the LCR meter is used to easily measure contact resistances of electronic components, such as coils, condensers, and resistors.
However, the LCR meter cannot avoid a measurement error. In particular, as the gate oxide layer of a MOS transistor becomes thinner, the measurement error becomes larger.
FIG. 1 is a flow chart illustrating a conventional method of determining a gate capacitance of a MOS transistor.
Referring to FIG. 1, a measured capacitance and a measured dissipation factor are obtained (step 110). Here, the measured capacitance and the measured dissipation factor are measured using an LCR meter. Next, a channel resistance and a tunneling resistance are obtained (step 120). The channel resistance and the tunneling resistance are obtained using a measured direct current of the MOS transistor via the transistor's equations.
An initial capacitance is set and a calculated capacitance is obtained (steps 130 and 140). The initial capacitance is a parameter used for finding the calculated capacitance and is arbitrarily set by a designer. That is, the initial capacitance is arbitrarily set and the calculated capacitance is obtained using an equation. Then, it is determined whether or not the obtained calculated capacitance is equal to the measured capacitance obtained by the LCR meter (step 150).
If it is determined that the calculated capacitance is not equal to the measured capacitance, a new initial capacitance is set, and steps 140 and 150 are repeated. Steps 130 through 150 are repeated until the calculated capacitance is equal to the measured capacitance. If the calculated capacitance is equal to the measured capacitance, the then initial capacitance corresponds to an accurate gate capacitance. Therefore, the initial capacitance is detected as the accurate gate capacitance (step 160).
However, as described above, as the gate oxide layer of a MOS transistor becomes thinner, the measurement error of an LCR meter becomes larger. Thus, in step 110, the measured capacitance itself may have an error. As a result, the accurate gate capacitance, obtained by the conventional method 100 shown in FIG. 1, may have an error.
When the gate capacitance is measured using an LCR meter, the number of measurement errors is proportional to the dissipation factor. Thus, to precisely correct a measurement error of the gate capacitance, an error of the dissipation factor must be precisely compensated.
Therefore, it would be desirable to provide a method of measuring an accurate gate capacitance by correcting a measurement error of a gate capacitance measured by an LCR meter, by correcting an error in the dissipation factor.